Interpretive Summary: The influence of management practices (tillage, nitrogen fertilization, and wheat cultivar) on the severity of leaf spot diseases on wheat was evaluated in a long-term cropping system project. Experimental treatments included all combinations of: 1) two cropping systems: spring wheat-fallow and annual cropping (spring wheat-winter wheat-sunflower); 2) three tillage treatments; 3) three nitrogen fertilizer levels; and 4) two cultivars of each crop grown. The most common leaf spot diseases were tan spot and Stagonospora nodorum blotch. In low precipitation years, the impacts of management practices on leaf spot disease severity were minimal. No-till did not consistently increase the severity of leaf spot diseases. During the drier years, no-till had the advantage of conserving soil water and did not increase the risk to leaf spot diseases. When nitrogen treatments influenced leaf spot diseases, higher levels of disease severity were associated with the low- nitrogen fertilizer treatment compared to higher levels of nitrogen fertilization. This indicates an advantage of using adequate nitrogen fertilizer especially with no-till under our environmental conditions. When leaf spot diseases were influenced by cultivar, Roughrider winter wheat had higher levels of disease severity compared to Norstar. The impact of cropping systems on disease severity of spring wheat cultivars (Stoa and Butte 86) was not clearly evident. Producers should integrate a combination of practices to develop a consistent long-term strategy for disease management suited to their production system and location.

Technical Abstract:
The influence of tillage, nitrogen fertilization, and cultivar on the severity of leaf spot diseases on wheat (Triticum aestivum L.) was evaluated in a long-term cropping system project. Experimental variables included all combinations of: 1) two cropping systems [spring wheat-fallow and annual cropping (spring wheat-winter wheat-sunflower (Helianthus annuus L.)]; 2) three tillage treatments [conventional till, minimum till, and no-till]; 3) three nitrogen (N) fertilizer levels for each cropping system; and 4) two cultivars of each crop grown. The most commonly isolated pathogens were Pyrenophora tritici-repentis (cause of tan spot) and Phaeosphaeria nodorum (cause of Stagonospora nodorum blotch). In low precipitation years, the impacts of management practices on leaf spot disease severity were minimal. No-till did not consistently increase the severity of leaf spot diseases. During the drier years, no-till had the advantage of conserving soil water and did not increase the risk to leaf spot diseases. When N treatments influenced leaf spot diseases, higher levels of disease severity were associated with the low-N fertilizer treatment compared to higher levels of N fertilization. When a tillage by N treatment interaction was significant, disease severity was higher with NT at the low N treatment but at the high N treatment the differences among tillage treatments were greatly reduced or eliminated. This indicates an advantage of using adequate N fertilizer especially with NT under our environmental conditions. When leaf spot diseases were influenced by cultivar, Roughrider winter wheat had higher levels of disease severity compared to Norstar. The impact of cropping systems on disease severity of spring wheat cultivars (Stoa and Butte 86) was not clearly evident. Producers should integrate a combination of practices (tillage, disease resistant cultivars and adequate fertility) to develop a consistent long-term strategy for disease management suited to their production system and location.